Input: bcm5974 - add support for the 2015 Macbook Pro

Add support for the MacBookPro12,1 model. This patch needs to be
applied together with the accompanied HID patch, as usual.

Tested-by: John Horan <knasher@gmail.com>
Tested-by: Jochen Radmacher <jradmacher@gmx.de>
Tested-by: Yang Hongyang <burnef@gmail.com>
Tested-by: Yen-Chin, Lee <coldnew.tw@gmail.com>
Tested-by: George Hilios <ghilios@gmail.com>
Tested-by: Janez Urevc <janez@janezurevc.name>
Signed-off-by: Henrik Rydberg <rydberg@bitmath.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>